Scientific Method —

Literacy may have stolen brain power from other functions

How do the specialized structures of the brain deal with an innovation— …

The human brain contains many regions that are specialized for processing specific decisions and sensory inputs. Many of these are shared with our fellow mammals (and, in some cases, all vertebrates), suggesting that they are evolutionarily ancient specializations. But innovations like writing have only been around for a few thousand years, a time span that's too short relative to human generations to allow for this sort of large evolutionary change. In the absence of specialized capabilities, how has it become possible for such large portions of the population to become literate?

The authors of a paper that will be released by Science today suggest two possible alternatives to explain this widespread literacy. Either reading is similar enough to something that our brains could already do that it's processed by existing structures, or literacy has "stolen" areas of the brain that used to be involved in other functions. (A combination of the two is also possible.) In the new paper, they use functional MRI imaging of brain activity to figure out just what literacy does to the brain, and discover that literacy does take over some new areas of the brain, with mixed effects on other areas of cognition.

The researchers point out that most of the studies on literature suffer from having a very biased study population. "Virtually all adult neuroimaging experiments are performed in highly educated college students," they note, before going on to explain that this extensive education can alter the brain in ways that makes the impact of literacy difficult to detect. So, they set up a study with three populations of Portuguese speakers: illiterate adults, those that have learned to read as adults, and a group that learned to read during their childhood education.

The subjects were given a battery of tests inside an MRI tube. Some involved simple visual patterns, like horizontal and vertical checkerboards, as well as images of faces and common items; others involved written and spoken sentences (some containing nonsense words); basic motor tasks and calculations rounded out the tests.

They were (as other studies have in the past) able to identify areas of the brain that were active during the processing of the written word. And the activity strongly suggests that formal schooling has little to do with matters. "The results were clear-cut," the authors write. "Virtually all of the above effects of literacy were present in ex-illiterates alphabetized during adulthood."

But the patterns in both these groups provide some indication of what's going on as literacy worms its way into our brains. Both simple visual patterns and text activated a similar area of the visual cortex, while both written and spoken words caused activity in both the temporal and frontal language areas. So, to some extent, literacy does seem to be taking advantage of brain structures that are already specialized for specific tasks.

However, the activity within the visual cortex was distributed differently in literate and non-literate individuals. A specific site, called the visual word form area, was activated by text to the exclusion of other categories, such as images or patterns. And that activity appears to induce some changes in other responses. Literate individuals seemed to have reduced activity when looking at images of faces. But they saw increased activity when looking at anything that vaguely resembles text, such as black-and-white images or checkerboard patterns with a horizontal orientation.

The decreased activity in response to faces seemed to occur in those who achieved literacy during childhood (it was one of the only differences between them and adult learners). The authors suggest that the area that responds to faces normally expands with age, and learning to read may limit this expansion by putting nearby brain areas to other uses.

This isn't to say that you're going to be worse with faces if you know how to read well, although the authors indicate they're going to look into that to find out. But it does indicate that literacy involves a new specialization in some areas of the visual system, which ensure that the centers involved with processing language become just as active as if they had heard the words spoken.